Method for measuring the damping coefficient of torsional-vibration dampers

Abstract

Measuring method for quickly checking the damping coefficient of torsion-vibration dampers filled with a viscous liquid and being provided with a swing ring. The basic principle relates to the recognition that there is a well measurable, numerically characterizable relation between the damping coefficient of a damper of a given nominal geometry and the number of vibrations of the freely oscillating system into which the damper being tested is fitted. An exemplary, preferred apparatus is described for carrying out the method. The method comprises the steps of determining permissible limit values of the torsional vibration damping coefficient in the vibration system; establishing a characteristic curve of a relation between the coefficient and the number of vibrations of the decay from a determined initial amplitude to a second determined amplitude within the vibration system; tuning the system by one of several expedients; producing the free oscillation with damping within the system; measuring the number of the vibrations in the system upon the characteristic curve; and taking the measured number as a basis between permissible limit values to verify the acceptable quality of the damper, while an inferior quality is being declared at measured values that lie outside the limit values.

What we claim is: 
     
       1. A method for quickly checking the damping coefficient of torsional-vibration dampers that are filled with a viscous liquid and are provided with a swing ring, for purposes of quality control of a damper of a given nominal geometry that is being tested, comprising the steps of: determining permissible limit values β'min and β'max of a torsional-vibration damping coefficient, between which values the quality of the damper is acceptable; establishing a characteristic curve of a relation between the damping coefficient and the number of vibrations of the decay from a determined initial amplitude to a second determined amplitude within a freely oscillating torsional-vibration system into which the damper is fitted for the testing, having one degree of freedom, i.e. which system includes a disc that constitutes a mass and a torsional shaft that constitutes a spring with a given stiffness; tuning the system by changing one of the mass of the disc and the spring stiffness of the torsional shaft to achieve a well measurable relation within the range of interest between the damping coefficient and the number of vibrations; producing free oscillation with damping within the system with the damper fitted in so that the free oscillation takes place with the determined initial amplitude; measuring the number of the vibrations in the system upon the characteristic curve and taking the measured number as a basis between permissible limit values n min  and n max  to verify an acceptable quality of the damper, while an inferior quality is being declared at measured values that lie outside the limit values. 
     
     
       2. The method as defined in claim 1, further comprising the step of using two of the torsional-vibration systems in order to perform said determining step, and for establishing a ratio of the coefficient of the damper being tested versus the optimum coefficient; the second system differing from the first one in respect of the spring stiffness of its torsional shaft, which stiffness is maximum half as much or at least twice as much as the stiffness of the first system. 
     
     
       3. The method as defined in claim 1, further comprising the steps of determining a damping coefficient β'opt of a plotted characteristic curve "number of vibrations versus a torsional damping coefficient β'" that is established in the system; and adjusting the system by said tuning step to achieve a relation of 1.5 β'opt<β'min. 
     
     
       4. The method as defined in claim 1, further comprising the step of comparing at the beginning of the free oscillation process one of the effective period time and of a proportional quality with a time Tβ'opt in order to perform said determining step, where Tβ'opt represents a period time of the damper being tested when it shows one of the optimum damping and a proportional quantity within that system which serves for control purposes.